Guide an autonomous approach

An autonomous approach links three jobs. Navigation estimates where the vehicle is and how it is moving. Guidance selects a desired path, and control changes the vehicle’s motion toward it. Accurate estimates alone do not guarantee a feasible path; a sensible path alone does not guarantee that the vehicle can follow it.

The March 22, 2024 LEX-02 experiment tested recovery from changed release conditions. ISRO describes corrections along and across the approach direction, followed by runway landing and deceleration. These are different errors: altitude, distance to the runway and displacement sideways should not be treated as interchangeable measurements.

In the June 23, 2024 LEX-03 experiment, the vehicle used multiple navigation inputs, including inertial measurements, radar altitude, air-data measurements, local navigation signals and NavIC. Combining measurements can improve an estimate when their uncertainties are understood. It does not mean that every input is independent or that agreement proves all sensors are correct.

Air-relative motion matters for aerodynamic behavior; ground-relative motion matters for reaching a place on the runway. In an original one-dimensional exercise, an aircraft travels forward at 90 metres per second relative to the air while facing a 10-metre-per-second headwind. Its forward ground speed is 80 metres per second. This simplified example ignores crosswind and is not a Pushpak operating instruction.

Connect navigation, guidance and control

A controller repeatedly compares estimated motion with the desired state and changes commands within the available authority. When wind or initial position differs, a correction must remain physically achievable. A flight record should preserve uncertainties and any saturation or limit events, rather than reporting only the final centerline position.

The runway-approach photograph shows the winged vehicle with its landing gear extended. It makes the terminal configuration visible; it cannot establish the quality of each sensor estimate. Trajectory records and test tolerances connect the visually striking landing to the claim that the autonomous system worked under specified conditions.